While this sounds interesting, note that now the galleria content has no html representation for e.g. search engines.
If we want to keep with that fallback, we should still add the output to the system and hide it...

I'm sticking this patch up because it fixes some undefined index issues that showed up with the above patch. And FYI the patch was tested with the latest dev versions of file_entity and media.

As for the html representation, the technique I used was to set the dataSource option for a data array created in the theme function. Basically it's like you see here. By setting this it overrides any html inside the galleria selector and hides it. I took out the html in part because it causes a flash of unformatted content (FOUC) on page load, and it's extra code that slows down rendering.

Should we make the adding the html a menu option?

As an aside, the patch has the array keys for the galleria layers and links, but they're commented out. It would be nice to get some input on how to best add these. I was thinking maybe we could add a link field and a textarea to file entities.

Add a content type with a file (not image) field and the media file selector widget (screenshot). Set up the field settings to allow image file types (with jpg, png extensions) plus video youtube and vimeo (screenshot).

Patch #5 is missing the fix on 'galleria-container.tpl.php' that is in patch #4.
I also had to make a change to the 'datasource'.... in the patch
// Add "data" array to galleria option "dataSource"
//$optionset->options['dataSource'] = $data;$optionset['options']['dataSource'] = $data;

Other modules, using the file module, have had similar errors ( http://drupal.org/node/845848 ) - and there it was a missing call to field_attach_submit.. but where that belongs in views.. plugin.inc - I have no idea :(

It works on well for me as I only use media-youtube. Also the size of the YouTube video should also render at a dimension that is the same as the "full" imagestyle settings, but that's beyond my knowledge.....

I just followed these instructions and wanted to provide the following feedback:

field_layer and field_link fields are not available in the existing field options (only Alt Text and Alt Title fields are available). If I manually create the field_layer and field_link fields, they are not recognized when setting the link and layer options in the Galleria field display options.

Encountered an internal server error when opening the media browser popup (media/browser) to add images/files. Luckily this can be solved by using the latest dev version of media_youtube module.

It is not possible to play the youtube video from within the lightbox popup as the left and right navigation arrows prevent the user from clicking directly on the youtube video. This can be resolved by reducing the width of the .galleria-image-nav-right and .galleria-image-nav-right elements using CSS.

Related to #3 in this list, the youtube videos when clicked will play in fullscreen mode. When this happens it is no longer possible to return to or close the lightbox popup or get back to the galleria page as the youtube layer is placed over the top of other page elements (even those with a higher z-index such as nav buttons. Tested with both Chrome and Firefox (actually using Iceweasel browser). Seems to only be a problem in firefox. Hopefully this can be fixed by adding "wmode=transparent" option to the youtube video URL. I am currently investigating which modules/code is responsible for generating the youtube video URL (haven't been able to track it down yet).